1. Field of the Invention
The present invention relates to an electrical heating type catalytic device.
2. Description of the Related Art
U.S. Pat. No. 3,770,389 discloses a conduction heating type catalytic converter wherein a columnar electrode is connected in the center of a metallic catalyst carrier, obtained by layering and winding a metallic corrugated sheet and flat sheet formed with insulation films on both surfaces so as to form alternate layers of corrugated sheet and flat sheet, a cylindrical electrode is connected at the outer periphery of the metallic catalyst carrier, a ceramic catalyst carrier is provided surrounding the metallic catalyst carrier, and a current is passed through the metallic catalyst carrier to heat it.
If the metallic corrugated sheet and flat sheet are joined by, for example, soldering, they become conductive, so if the corrugated sheet and the flat sheet are joined over the entire region of the metallic catalyst carrier, the electrical resistance of the metallic catalyst carrier falls too low and almost no heat is generated even if current is passed through them. Therefore, in the above-mentioned conventional catalytic converter, the corrugated sheet and the flat sheet are not joined over the entire region of the metallic catalyst carrier, whereby the metallic catalyst carrier is given an electrical resistance suitable for heat generation from the columnar electrode to the cylindrical electrode.
However, in this catalytic converter, since the corrugated sheet and the flat sheet are not joined over the entire region of the metallic catalyst carrier, when the catalytic converter is mounted in the exhaust system of an internal combustion engine and exposed to high temperatures, the temperature difference in the metallic catalyst carrier gives rise to thermal stress which causes a deviation of the corrugated sheet and flat sheet in the axial direction of the metallic catalyst carrier in addition to deviation derived from the exhaust pressure. Once this deviation occurs, it rapidly increases and gives rise to the problem of destruction of the metallic catalyst carrier.